Water distribution systems of the just mentioned type are known in commercial aircraft in order to supply hand wash basins in toilets and sinks in onboard kitchens with fresh water. Frequently fresh water is also used for flushing toilet basins. Water that has been used in a hand wash basin and in a kitchen sink becomes waste water and is conventionally discharged from the aircraft into the environment. However, sewage is collected in a waste water tank which may also receive used waste water. Normally, the discharge of waste water takes place with the aid of reduced pressure creating a suction effect in the toilet facilities for conveying the sewage to the collection tank.
Conventional fresh water supply systems have the disadvantage that the supply tank or tanks are connected to the respective facilities by a one-way main line. The term "line" as used herein is intended to cover any suitable pipe or duct. A one-way main line is always filled with water even when water is not used. Further, these lines, as a rule, are installed in the or near to the aircraft bottom that separates a freight space from a passenger cabin.
As a result, the line is exposed to a cold environment, especially when the aircraft is travelling at high elevations. As a result, freeze-up of the water supply lines is possible, unless the lines are heated, for example by electrical heating elements installed in parallel to the water lines. This type of construction is involved and expensive in its manufacture and installation.
It is also conventional to provide these water lines with a continuous inclination for draining the system by gravity flow. Inclined lines cause difficulties when a basic aircraft type is modified to produce a shorter or longer version of the basic type. In both instances substantial problems arise in installing the lines with the required inclination. In these instances assuring the required line inclinations makes it necessary to redesign the line installation with due regard to the available structural length of the aircraft, or rather the length available for the line installation.